low coherence interferometry: from sensor multiplexing to biomedical imaging

Low Coherence Interferometry: From Sensor Mul7plexing to

Biomedical Imaging

António Lobo (PhD, MSc, EMBA)

Summer School AOP 2012

Porto, June 28-‐29, 2012

Outline §  Some history…

§  LCI in op7cal fiber sensors • General concepts •  Sensor mul7plexing

§  LCI in medical imaging • Op7cal Coherence Tomography (OCT) • OCT op7cal sources • OCT modali7es

Some history... §  Low Coherence Interferometry: Sensing Applica7ons

•  1983 – Al-‐Chalabi, B. Culshaw, D.E.N. Davies, Univ. College London, UK (First Interna7onal Conference on Op7cal Fiber Sensors, OFS’1, London)

•  First demonstra7on of the coherence mul7plexing in sensors •  The system was not patented !

Some history... §  Low Coherence Interferometry: Metrology

•  1987 – R. Youngquist, S. Carr, D.E.N. Davies – Op#cs Le)ers 12 (3), 158-‐160. •  First demonstra7on on optoelectronic metrology •  Op#cal Coherence-‐Domain Reflectometry (OCDR)

Some history... §  Low Coherence Interferometry: Medical Applica7ons

•  1986 – A. Fercher, E. Roth, Medical Univ. Vienna, Austria (SPIE Conference on Op#cal Instrumenta#on for Biomedical Laser Applica#ons)

•  1988 – A. Fercher, K. Mengedoht, et.al. -‐ Op#cs Le)ers 13 (3), 186-‐188. •  Par#ally Coherence Interferometry

Some history... §  Low Coherence Interferometry: Medical Applica7ons

•  1986 – J. Fugimoto, et.al., M.I.T., USA. -‐ Op#cs Le)ers 11 (3), 150-‐152. •  Intensity Correla#on •  1991 – J. Fujimoto, et.al. – Science 254, 1178-‐1181. •  1st image in-‐vitro – Op#cal Coherence Tomography (OCT)

1st Human re7na (in-‐vitro) OCT image [axial resolu7on: 15 μm, wavelength. 830 nm]

General Concepts §  Low Coherence (or “white-‐light”) Interferometry

DC terms

auto-‐correla7on terms

cross-‐correla7on terms (important for Imaging)

E(t) = Eref (t)+ Esampl (t +τ n )n∑ =

= Eref (t)+ Esampl (t + Δzn c)n∑

I = E*(t) ⋅E(t)

I(τ ) = I0 ar + ann∑⎡

⎣⎢⎤⎦⎥+

+2I0 anam Re γ ss (τ nm ){ }m≠n∑ +

+2I0 anar Re γ (τ n ){ }n∑


func7on that depends on the source spectrum profile

Coherent source (ideal laser)

low coherence source (LED, SLD, Lamp,…)

axial posi7on, z axial posi7on, z OPD: Op7cal Path Difference

I(τ r ) = Const + 2I0 anam ⋅ γ (τ n )n∑ ⋅cos(ωτ n )

γ (τ ) = γ (τ ) e− iωτ

cos(ωτ n ) = cos 2πνnΔzc

⎛⎝⎜

⎞⎠⎟ = cos

2πλnΔz⎛

⎝⎜⎞⎠⎟


•  Why? §  Sensor ini7aliza7on on “powering-‐up” §  Non-‐ambiguous dynamic range can be very large §  The system can be operated such that:

§  (a) the measurement accuracy is independent of the source stability §  (b) the effects of wavelength instability of the source are greatly reduced

§  The output signals from many sensors can be mul7plexed §  Remote sensor tracking possible (tandem configura#on) §  No op7cal isolator required (…in principle!!)

•  Problems? §  In “tandem configura7on” requires a second stable interferometer §  Op7cal power available from typical short coherence sources are low

General Concepts §  Low Coherence Interferometry: Tandem Configura7on

ΔLR ΔLS LCS

IDI0

≈ 1+ γ (ΔLS ) cos2πnλ

ΔLS⎛⎝⎜

⎞⎠⎟+ γ (ΔLR ) cos

2πnλ

ΔLR⎛⎝⎜

⎞⎠⎟+ 2 γ (ΔLS ± ΔLR ) cos

2πnλ(ΔLS ± ΔLR )

⎛⎝⎜

⎞⎠⎟

•  LCS with Gaussian spectrum •  ΔLS >> coherence length of LCS!


•  LCS is mul7mode laser diode •  ΔLS >> coherence length of LCS!

ΔLR ΔLS LCS

A.S. Gerges et.al., Appl. Opt. 29, 4473-‐4480 (1990). A.B. Lobo Ribeiro et.al.,Rev. Sci Instrum.63, 3586-‐3589 (1992)


•  How to extend further the non-‐ambiguous dynamic range?

LCS @ λ1

LCS @ λ2

ΔLR ΔLS

φ1 =2πnλ1(ΔLS − ΔLR )

φe =2πnλe

(ΔLS − ΔLR )

λe =λ1λ2

λ1 − λ2A.B. Lobo Ribeiro et.al., Opt. Commun.109, 400-‐404 (1994).

Op7cal Sources for LCI §  Ideal characteris7cs for fiber sensors

•  High output op7cal power •  Wavelength emission around 1550 nm (3rd telecom window)

•  Smooth (no ripple) “Ideal” Gaussian spectrum profile

•  Spectral bandwidth (FWHM) larger as possible

•  Non-‐polarized output •  Spectrally stable against back-‐reflec7ons (op7cal isolator?) •  Singlemode Fiber op7c pigtailed

•  Low cost (… as always!!)

Op7cal Sources for LCI §  Light-‐Emiwng Diode (LED)

•  Low output power in fiber (μW) •  MM or SM fiber pigtailed

S-‐LED IRE-‐161 λ = 830 nm Δλ = 45 nm

Measured with a Michelson interferometer

Normalize

d visib

ility fu

nc7o

n

OPD (μm)

Op7cal Sources for LCI §  Mul7mode Laser Diode (MM-‐LD)

•  High output power in SMF pigtailed fiber •  But…imposes some opera7onal restric7on on sensor OPD

Normalize

d visib

ility fu

nc7o

n

OPD (mm)

Measured with a Michelson interferometer

Op7cal Sources for LCI §  Superluminescent Diode (SLD)

•  “High” output power in fiber (2 to 25 mW, depending on λ) •  Singlemode fiber pigtailed

Courtesy of Superlum Ltd.

Op7cal Sources for LCI §  ASE Fiber Sources

•  High output power on fiber (>50 mW) •  Central wavelength emission (typ.): 1550 nm, 1060 nm

Courtesy of Mul7wave Photonics S.A.

Dimensions (mm): 120 x 90 x 22.2"

LCI in Sensor Mul7plexing §  Coherence Division Mul7plexing (CDM)

•  Each sensor must have different OPD •  Receiver interferometer needs large tuning range •  Demonstrated with polarimetric sensors

ΔLR

ΔL1 LCS

ΔL2

J.L. Santos and A.P. Leite, Proc. Conf. OFS’9, 59-‐62 (1993). A.B. Lobo Ribeiro et.al., Fiber & Integrated Op7cs 24, 171-‐199 (2005)

S1

S2

LCI in Sensor Mul7plexing §  CDM + Spa7al Division Mul7plexing (SDM)

•  Each sensor can have iden7cal OPD •  Receiver interferometer needs smaller tuning range

ΔLR ΔL1

LCS

ΔL2

A.B. Lobo Ribeiro et.al., Proc. Conf. OFS’9, 63-‐66 (1993).

LCI in Sensor Mul7plexing §  CDM + Wavelength Division Mul7plexing (WDM)

•  Simultaneous measurement: Displacement + Temperature •  Interroga7on of small Fabry-‐Perot cavity (for displacement)* •  Fiber Bragg Gra7ng (FBG) match-‐pair technique (for temperature)**

(*) L.A. Ferreira et.al., IEEE Photon. Technol. Le|. 8, 1519-‐1521 (1996). (**) A.B. Lobo Ribeiro et.al., Appl. Opt. 36, 934-‐939 (1997).

Receiver Sensor

FBG

FP Cavity

LCI Processing §  Phase Domain Processing

•  Fringe pa|ern analysis is done by measuring the op7cal phase varia7on: §  Temporal fringe processing (modula7ng the OPD of the receiver interferometer) §  Spa7al fringe processing (CCD detec7on and fringe coun7ng)

•  OPD of the sensing interferometer must be greater than coherence length of the source ⇒ no interference is observed.

LCI Processing §  Spectral Domain Processing

•  Fringe pa|ern analysis is done using a Op7cal Spectrum Analyzer (OSA) •  Free spectral range (FSR):

Normalize

d ou

tput

Wavelength, λ (nm)

Gaussian source:

FSRλ =

λ02

nΔL

LCI on Optoelectronic Metrology §  Op7cal Low Coherence Reflectometry (OLCR)

W.V. Sorin, et.al., IEEE Photon. Technol. Le|. 4, 374-‐376 (1992). F.P. Kapron, et.al., J. Lightwave Tech. 7, 1234-‐1241 (1989).

Low Coherence Imaging §  OLCR on Biomedical Applica7ons?

•  Proper choice of op7cal source is necessary. §  Wavelength §  Spectral bandwidth §  Output op7cal power

Biological 7ssue

Low Coherence Imaging §  Op7cal Coherence Tomography (OCT)

•  Already an establish medical imaging technique •  Ophthalmology, Cardiology, Dermatology, etc.

1D Axial scanning (Z)


Transverse scanning (X)


XY Scanning

Backreflected intensity

Axial posi7on (penetra7on depth)

W. Drexler and J.G. Fugimoto, Op#cal Coherence Tomography: Technology and Applica#ons, Springer, 2008

Low Coherence Imaging §  Op7cal Coherence Tomography (OCT)

•  Resolu7on Limits §  Wider source spectrum ⇒ Higher axial resolu7on §  Higher Numerical Aperture (NA) ⇒ Large transverse resolu7on

High NA

low NA

Δx

Δz

b

Δz = 2 ln2π

⋅ λ2

ΔλΔx = 4λ

π⋅ fD

b = 2zR =πΔx2

λ

Axial Resolu7on Transverse Resolu7on

Depth Focus

Low Coherence Imaging §  Op7cal Source for OCT

•  Large spectral bandwidth ⇒ axial resolu7on •  Adequate central wavelength ⇒ absorp7on 7ssue curve •  Adequate spectral profile ⇒ Gaussian profile •  Enough op7cal power ⇒ be|er SNR

Δλ Δz

Δz = 2 ln2π

⋅ λ2

Δλ

Low Coherence Imaging §  Op7cal Source for OCT

•  Op7cal window of biological 7ssue

new im

aging windo

w

800 900 1000 1100 1200 13000,00

0,05

0,10

0,15

0,20

0,25

0,30 Kou et al., Applied Optics, 32, 19, 3531-3540, 1993

Wat

er A

bsor

ptio

n C

oeffi

cien

ts (2

2o C) (

mm

-1)

Wavelength (nm)

~100 nm

Low Coherence Imaging §  Op7cal Sources for OCT

Superluminescent Diode (SLD)

MQW Semiconductor Op7cal Amplifier (MQW-‐SOA)

ASE Doped Fiber Sources

KLM Solid State Laser

Incandescent Light Sources

Supercon7nuum Sources

Spectral BW

Spectral region

Output power

Op:cal stability

+ + ~ ++ ++ Dimensions

+ + + + +

+ ~ +++ ++ ++

++ ++ ++ + ~

+++ + -‐-‐ + ~

+++ +++ ++ ~ ~

Courtesy ( in part) from Prof. W. Drexler


•  Most common used in commercial systems: SLD

λ0 = 870 nm Δλ = 180 nm

P0 = 5 mW

Superlum Ltd., Ireland

180 nm 2.5 μm


•  Mostly used in R&D systems: fs-‐KLM Ti:Sapphire laser

Ophthalmic OCT exam (courtesy of Prof. W. Drexler)

FEMTOLASERS Produk7ons GmbH, Vienna, Austria

90 cm

45 cm

W.Drexler, et.al., Opt.Le|.24(17),1221-‐1223 (1991).

λ0 = 800 nm Δλ = 165 nm

Pavg = 40 mW

Low Coherence Imaging §  Higher depth penetra7on into the eye?

•  1060 nm wavelength region §  Local minimum in water absorp7on §  Lower sca|ering 7ssue coefficient §  Zero dispersion point of water §  ANSI standard ~2 mW for 10 s exposure 7me

B. Povazay, et.al., Opt.Express 17 (5), 4134-‐4150 (2009)

840 nm 1060 nm Eye Fundus

SLD source ASE Doped-‐Fiber source


•  ASE fiber sources @ 1060 nm §  Yb-‐doped fiber (usually used as gain media) §  Careful op7c design to avoid undesired laser emission §  Spectral tailoring maybe necessary

A.B. Lobo Ribeiro, et.al., in Proc. SPIE vol.7139 (U.K., 2008), p.713903.


•  ASE Yb-‐doped fiber source §  Spectral bandwidth: 50 nm (typ.) §  Output power (fiber): >50 mW

9.7 µm!

A.B. Lobo Ribeiro, et.al., in Proc. SPIE vol.7139 (U.K., 2008), p.713903.


•  ASE fiber sources @ 1060 nm §  Broader spectral bandwidth ⇒ other doped-‐fiber combina7ons

A.B. Lobo Ribeiro, et.al., US Patent 20100315700(A1), Dec. 2010

-50 -40 -30 -20 -10 0 10 20 30 40 500,0

0,2

0,4

0,6

0,8

1,0

Nor

mal

ized

inte

rfer

ogra

m

Optical path difference (µm)

7 µm

1000 1020 1040 1060 1080 1100 1120-35

-30

-25

-20

-15

-10

-5

0

λ0=1058.124 nm

ΔλFWHM = 71.209 nm

Pout= 21,3 mW

Pow

er d

ensi

ty (d

Bm

/nm

)

Wavelength (nm)

ASE Yb+Nd-‐doped fiber source

Low Coherence Imaging §  ASE Yb+Nd-‐doped fiber source

•  TD-‐OCT system @ 1 μm §  With confocal channel §  En-‐face and cross sec7onal OCT images §  15 μm lateral resolu7on §  < 15 μm axial resolu7on §  2 Hz frame rate

I.Trifanov, et.al., IEEE Photon. Technol. Le|. 23, 21-‐23 (2011).

Low Coherence Imaging §  ASE Yb+Nd-‐doped fiber source

•  TD-‐OCT system @ 1 μm

I.Trifanov, et.al., IEEE Photon. Technol. Le|. 23, 21-‐23 (2011).

Choroid

100 µm RNFL"

GC/IPL"INL"OPL"ONL"ELM"

RPE"Ch/Chc"

IS/OS"

RNFL: re7nal nerve fiber layer; GC/IPL: ganglion cell/inner plexiform layer; INL: inner nuclear layer; OPL: outer plexiform layer; ONL: outer nuclear layer; ELM: external limi7ng membrane; IS/OS: photoreceptor inner segment/outer segment junc7on; RPE: re7nal pigment epithelium; Ch/Chc: choroid/choriocapillaris

Cross sec7onal OCT images of re7na

Low Coherence Imaging §  Other OCT Modali7es: Fourier Domain OCT

Spectral Domain OCT (SD-‐OCT) Swept Source OCT (SS-‐OCT)

M. Wojtkowski, Appl. Opt. 49 (16), D30-‐D60 (2010).

Low Coherence Imaging §  Human Choroid 3D-‐OCT image

•  SS-‐OCT system @ 1 μm

Courtesy of Prof. Y. Yasuno

Y. Yasuno, et.al., Opt. Express 15 (10), 6121-‐6139 (2007).

Low Coherence Imaging §  Swept Fiber Laser @ 1060 nm

•  Central wavelength: 1065 nm •  Sweeping frequency: 1-‐ 8 kHz

A.B. Lobo Ribeiro, et.al., US Patent 2011069722(A1), Mar. 2011 I. Trifanov, et.al., in Proc. SPIE vol.7899,Photonics West 2011, pp.7899-‐100 (2011).

Low Coherence Imaging §  OCT System with Swept Source @ 1060 nm

I. Trifanov, et.al., in Proc. SPIE vol.8091, BIOS Europe 2011, pp.8091-‐30 (2011).

Human tooth with lead implant (B-‐scan)

0 mm depth 2.5 mm depth 5 mm depth

Acknowledgements §  UOSE/INESC-‐TEC & Physics Dept., FCUP (PT)

•  Prof. José Luís Santos •  UOSE R&D Team

§  AOG, School Phys. Sci., Univ. Kent (UK) §  Prof. Adrian Podoleanu §  Prof. David Jackson §  AOG R&D Team

§  Mul7wave Photonics S.A. (PT) §  Prof. José Salcedo §  R&D Team

§  CMPBE, Medical Univ. Vienna (Austria) §  Prof. Wolfgang Drexler §  Dr. Boris Povazay

§  COG, Tsukuba Univ. (Japan) §  Prof. Yoshiaki Yasuno

Thank you for your a|en7on

low coherence interferometry: from sensor multiplexing to biomedical imaging

Technology

coherence mul7plexing

ally coherence interferometry

ls lr cos2nls lr lcs

tandem congura7on lcs

eref t esampl t n n

op7cal sources

const 2i0 anam n n cos

ls cos2nls lr cos2nlr